[BlueOnyx:14671] Re: error (0x800CCC80): - WORKAROUND

[Michael Stauber]

Hi Dan,

>  can now see the cipher changes in /etc/dovecot/conf.d/10-ssl.conf
> 
> I have managed to get my customers working again by changing the 
> ssl_cipher_list to the following based on this blog post... 
> http://jasonbrown.us/blog/disable_weak_cipher_dovecot
> 
> ssl_cipher_list = 
> ALL:!LOW:!MEDIUM:!MD5:!SSL2:!EXP-ADH-DES-CBC-SHA:!EXP-EDH-RSA-DES-CBC-SHA:!EXP-DES-CBC-SHA:!EXP-EDH-RSA-DES-CBC-SHA:!EXP-ADH-DES-CBC-SHA:!EXP-DES-CBC-SHA:!ADH-AES256-SHA:!ADH-AES128-SHA:!ADH-DES-CBC3-SHA:!EXP-ADH-DES-CBC-SHA:!EXP-ADH-DES-CBC-SHA:!ADH-DES-CBC3-SHA
> 
> Michael, I'm sure you spent ages coming up with your cipher_list.  It 
> seems it's too restrictive :-/

Sorry, but the cipher list you quote above is not really making much
sense. I'm even a little tempted to say they're utter nonsense, knowing
that they're not your ciphers, but some you found on the internet.

You see, these ciphers above allow everything and then selectively
disable protocols that use SHA for checksums. It even disables
ADH-AES256-SHA, which out of the disallowed lot is one of the better ones.

That approach is in so far total nonsense, as he leaves RC4 enabled,
which is known to be compromised. It also leaves 3DES, PSK and DSS based
ciphers active, which also have a shady history.

But worst of all: He leaves the EXP ciphers active. That's the OpenSSL
ciphers for Export. 40-bit stuff. Not 2048-bit. No, I mean 40-bit.

If that guy leaves the Export ciphers active, he doesn't know what he's
doing. Or he works for the NSA. BEEEP. Disqualified. :-)

For Dovecot we're using the crypto ciphers recommended on
https://bettercrypto.org/ and for Apache we're using a slightly modified
version of that. It's as good as it gets. It forces clients to use the
most secure protocols first and if negotiation fails for that, there is
usually a common denominator somewhere at the bottom of the acceptable
range of ciphers.

But yes: They are known to give XP users the short end of the stick. For
a reason. The internet would be a lot better place if all that XP boxes
still around and hooked up to it would just roll over and die.

> This is affecting an Outlook 2007 user on WinXP (I know) and an
> Entourage user on Mac.

You see, I recently asked my bank why their online banking still allows
RC4 and allows no "perfect forwarding secrecy". I didn't expect a reply,
but their IT department sent back a lengthy explanation which boiled
down to one apologetic line: "We still have to allow XP users in."

That's exactly what's wrong: These lazy gits (who haven't heard the shot
yet) are lowering the security of everyone around them.

So: No, sorry and really no hard feelings. But I won't punch a security
hole into our ciphers for just two users with ancient email-software.

Feel free to use whatever work around you feel necessary to still allow
them in.

-- 
With best regards

Michael Stauber